Out of the Lab, Into the Frying Pan: Understanding the Effect of Natural Groundwater Conditions on Bio-Based Ground Improvement Strategies

We are developing a biogeochemical model for microbial denitrification-driven ground improvement to account for t the complexities expected in the field, including microbial inhibition and competition. We will use this model to support Microbially Induced Desaturation and Precipitation (MIDP) via denitrification as a bio-based ground improvement strategy alternative considering different treatment recipes and natural groundwater composition. Current ground improvement techniques have limited utility underneath or near existing structures. Developing alternatives is becoming increasingly important as urbanization increases. Large, centralized populations and infrastructure are more vulnerable to threats by natural disasters and geologic hazards such as earthquake-induced liquefaction and flooding. Bio-based ground stabilization techniques may be less disruptive to deploy and monitor, allowing application underneath existing structures. MIDP is a two-stage ground-improvement process in which biogenic gas desaturation provides immediate improvement while calcium carbonate precipitation provides long term stability. MIDP influences the geochemical environment and the hydro-mechanical behavior of soils through biogenic gas production, precipitation of calcium carbonate, and biomass growth. All three components alter the biogeochemical environment and subsurface permeability, thereby affecting the transport of substrates and subsequent product formation. The products of MIDP mitigate liquefaction at the lab-scale. MIDP experimentation and modeling have primarily considered only the use of de-ionized water and simplified water composition. However, denitrifying microorganisms compete with alternative electron acceptors, like sulfate and iron, and are influenced by the environment’s pH and salinity which may impede the MIDP treatment. Our biogeochemical model can predict the products and by-products of MIDP treatment considering realistic groundwater conditions. The results of this model will be used to develop comprehensive treatment plans for upcoming field trials to demonstrate treatment effectiveness and develop best practices for future application.